This invention relates to the field of oil and gas recovery and in particular to devices and methods for improving the production of new or existing wells by fracturing geological structures adjacent the well bore at the particular production zones in which flow to the well bore is to be stimulated.
In the past, the most common formation fracturing method for stimulating production has comprised the separate step method of projectile penetration of the production zone and hydraulic pressurization of the well using high pressure pumps to induce expansion or propagation of projectile initiated fractures. The substantial expense of preparing the well to receive the pumped fluid without collateral zone leakage and the time and expense of pumping fluids at the high pressures necessary for fracture expansion of the desired zones make this method unattractive for most low producers or multiple zone wells.
Gas propellants have been employed as a less expensive substitute to hydraulic fracture propagation. Again, the procedure has comprised the separate step method of projectile penetration of the production zone followed by a separate treatment with propellant devices. The separate step treatment using such techniques in cased wells has been almost exclusively perforated to the specifications of hydrafrac such that subsequent use of propellant frac requires an additional perforation step to provide adequate points of entry. Further, open hole treatments have rarely, if ever, used the perforation technique whether hydrafrac or propellant frac. The propellants have been generated by a variety of charge forms: pulsating charges, multiple point initiation of charges, uniformly burned charges, fast combustion (greater than sound speed in the well fluids), slow combustion (slower than sound speed in the well fluids), long cylindrical charges, short cylindrical charges, etc. These gas propellant charges have been used to expand zones previously perforated and have been successful.
It is a general object of this invention to provide a method and apparatus for stimulating oil or gas production in a drilled well that increases the effectiveness of propellant fracing at a substantial cost saving to the operator in both time and money. In using a gas propellant it is a further object to maximize the delivery potential of the propellant correlative to propagation of fracture and to maximize the effectiveness of the resultant fracture for enhanced production.